Metal particles in the micron scale range are important to large industries including the paint industry, the metal parts manufacturing industry, etc. Parts made with metal particles can be complex in shape. For example the metal powder can be introduced into a die and sintered, or can be made by laser sintering layers built one layer at a time using 3-D printing devices. These parts are useful for appliances, bearings and gears, cutting tools, filters, and electrodes.
Conventional production technologies for making micron scale metal particles include atomization, electrolysis, plasma spray, and solid state reduction, in atomization, molten metal is forced through nozzles to form liquid jets. These jets are rapidly cooled with water or inert gases to create particles. Consequently, purity is compromised by the inclusion of oxygen gettering species in the molten metal. In addition, this process is energy inefficient. For example, only about 1% of the pumping energy actually goes into particle formation. Electrolysis requires a variation on the standard electrolytic processes, such that particles rather than films are produced at an electrolytic cell cathode. Consequently, this process is limited to particular metals, as it requires dissolution of metal, which is often expensive. In solid state reduction, finely ground oxide particles are treated with reducing gases, at a temperature lower than the melting point of the metal to produce reduced and sintered particles. Consequently, the metals created using this multi-step method have relatively high impurity levels. Plasma spray technology does yield high purity particles of controlled shape. However, it is not widely used because the technology is inherently energy intensive, and requires expensive, sophisticated equipment.
Production of metal particles in the nanometer scale have been introduced in the last decade by methods including sono-chemistry, wet chemistry methods, co-precipitation micro-emulsion methods, and laser-driven thermal methods. Other methods for making metal particles include metal gas evaporation, metal evaporation in a flowing gas stream, mechanical attrition, sputtering, electron beam evaporation, electron beam induced atomization of binary metal azides, expansion of metal vapor in a supersonic free jet, and pyrolysis of organometallic compounds. However, all of these methods face obstacles of contamination, expensive processes, low yields, and difficulty of mass production and industrial up scaling.
It is thus desirable to provide a method/process capable of producing zero valent metal/metal alloy particles in the micron, sub-micron, and/or nanometer size range.